Mendenhall plant moves toward future

Improvements and operational changes aimed at efficiency

Posted: Sunday, August 05, 2001

The swirl of sewage inside the basins at the Mendenhall Wastewater Treatment Plant indicates that the facility is operating better than ever, according to city officials.

About 2 million gallons of raw sewage are treated the Mendenhall Plant each day, said Roger Hulse, supervisor at the Mendenhall and Auke Bay treatment plants. He points to beakers of fluid collected before and after treatment. The first is brown and murky. The second is crystal clear.

"The plant's running fantastic," he said.

Designed in 1985, the Mendenhall plant was completed in 1990 under a U.S. Environmental Protection Agency program for innovative, alternative treatments. The program provided bigger grants for unproven technologies to encourage innovation in wastewater treatment, according to a report from engineering and environmental consulting firm Carson Dorn Inc.

Over the past two years, the city has spent more than $1 million in capital improvements and made operational changes at the plant to address odor and treatment challenges, according to the report.

A tour through the facility gives a picture of the changes. New decanters prevent problems that required sewage to be sent elsewhere in the plant for retreatment. A centrifuge helps reduce odor. New indicators give the plant's operators a better idea of the type and level of material in the basins, and they require less maintenance. A new computer system and testing procedures help track the flow of waste.

A consultant who inspected the Mendenhall plant for the city in March found that security procedures should help prevent potential tampering with effluent samples, according to a report from engineering firm CH2M Hill.

"The city has instituted a security system and procedures that provide a high probability of obtaining reliable representative effluent data free from tampering," project specialist George Mason found.

Under changes implemented in early 2000, samples are removed from the plant by two operators. Each sample is signed and sealed, then taken to an independent lab for testing. All operators are involved in sampling on a rotating basis. Video cameras monitor the sampling areas inside the plant, according to the report.

An EPA permit for the Mendenhall plant issued in March included new testing requirements. Using a 16-foot boat, workers collect 12 samples downstream in the Mendenhall River on a regular basis. Additionally, the plant runs a host of other tests for fecal coliform, metals and solids, Hulse said.

The proof of the plant's turnaround is the quality of treated effluent that leaves the plant, consultant Jim Dorn said. Tests for total suspended solids and biological oxygen demand both good indicators of a plant's effluent quality should be at 30 parts per million or below, he said. In June, the average biological oxygen demand level was 8.2 parts per million. The total suspended solids average was 7.8, according to discharge monitoring reports.

Metal levels have been one area of focus for the plant, Hulse said. Like many other wastewater treatment plants in the country, the Mendenhall facility has reported high levels of copper, likely due to copper sewer pipes that run to the facility. The plant has notified the EPA about the issue, set up a "clean room" to reduce contamination and is working on other changes.

Longer term, Public Works Director Ernie Mueller said the city hopes to install an ultraviolet disinfection system at the plant to help eliminate the need for hazardous disinfection chemicals. The city also plans to add another blower and replace the structure that discharges effluent into the river, he said.

More information about the city's wastewater utility division is available on the Web at The site includes the latest discharge monitoring reports and other information.


Joanna Markell can be reached at

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